Photographic products and processes employing pH sensitive filter dyes
US4139381A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 23, 1977 |
| Grant date | Feb 13, 1979 |
| Priority date | — |
| Expiry date | Sep 23, 1997 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03C8/48
- WIPO fieldOrganic fine chemistry
- WIPO sectorChemistry
Abstract
This invention is concerned with photographic products, particularly diffusion transfer photographic film units, useful in photographic processes conducted outside of a camera wherein post-exposure fogging by ambient light is prevented by a compound initially present as a substantially colorless compound which is activated by base to provide a light-absorbing reagent or colored optical filter agent which is capable of being irreversibly discharged without a change in pH. The colorless compound or filter agent precursor is initially disposed in a layer of the film unit, for example, in a layer coated over the photosensitive element. Subsequent to imagewise exposure of the photosensitive element, the colored optical filter agent is generated by contacting the colorless precursor with a basic processing composition. After remaining in contact with said basic composition for a given time, the colored optical filter agent is discharged by forming a new compound which is substantially colorless and which is different from and non-reversible to said precursor and different from and non-reversible to said optical filter agent.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.